Determination of time- and height-resolved volcanic ash emissions and their use for quantitative ash dispersion modeling: the 2010 Eyjafjallajökull eruption

Abstract

Abstract. The April-May, 2010 volcanic eruptions of Eyjafjallajökull, Iceland caused significant economic and social disruption in Europe whilst state of the art measurements and ash dispersion forecasts were heavily criticized by the aviation industry. Here we demonstrate for the first time that large improvements can be made in quantitative predictions of the fate of volcanic ash emissions, by using an inversion scheme that couples a priori source information and the output of a Lagrangian dispersion model with satellite data to estimate the volcanic ash source strength as a function of altitude and time. From the inversion, we obtain a total fine ash emission of the eruption of 8.3±4.2 Tg for particles in the size range of 2.8-28 µm diameter. We evaluate the results of our model results with a posteriori ash emissions using independent ground-based, airborne and space-borne measurements both in case studies and statistically. Subsequently, we estimate the area over Europe affected by volcanic ash above certain concentration thresholds relevant for the aviation industry. We find that during three episodes in April and May, volcanic ash concentrations at some altitude in the atmosphere exceeded the limits for the "Normal" flying zone in up to 14 % (6-16 %), 2 % (1-3 %) and 7 % (4-11 %), respecCorrespondence to: A. Stohl (ast@nilu.no) tively, of the European area. For a limit of 2 mg m −3 only two episodes with fractions of 1.5 % (0.2-2.8 %) and 0.9 % (0.1-1.6 %) occurred, while the current "No-Fly" zone criterion of 4 mg m −3 was rarely exceeded. Our results have important ramifications for determining air space closures and for real-time quantitative estimations of ash concentrations. Furthermore, the general nature of our method yields better constraints on the distribution and fate of volcanic ash in the Earth system.

Uncertainties in the inverse modelling of sulphur dioxide eruption profiles

“…Within the SAVAA project, our method has also been extended to volcanic ash (Stohl et al 2011). It has become obvious in the context of the Eyjafjallajo¨kull spring 2010 eruption that a better definition of the source term could be very important for efficient support of VAAC operations, which came under heavy criticism from the aviation industry.…”

“…Especially in near-realtime and for volcanoes that are not monitored well, detailed knowledge of eruption source parameters is lacking. Furthermore, simple models are not very accurate (Stohl et al 2011) while very complex models like ATHAM (Active Tracer High Resolution Atmospheric Model, Herzog and Graf 2010) are unsuitable for near-real time operations. Any simulation of gas or ash transport from a volcanic eruption, at the spatial scales for which the method is applicable, will benefit from our inversion results.…”

“…A larger observation uncertainty as in figure 8, which can be thought of as including a transport uncertainty contribution, counteracts this. Better quantification of transport uncertainty (Stohl et al 1995;Seibert 2000Seibert , 2009Stohl et al 2011) should thus be helpful to obtain better inversions.…”

“…However, they have not attempted to do a time-resolved Uncertainties in the inverse modelling of SO 2 eruption profiles 203 inversion. Our methodology has only recently been expanded to include a temporal dimension in the source term (Stohl et al 2011).…”

“…The method has so far been applied to sulphur dioxide emissions from Jebel at Tair (Eckhardt et al 2008), Kasatochi (Kristiansen et al 2010), and -in expanded form -Eyjafjallajo¨kull (Stohl et al 2011). It is based on SO 2 satellite column data obtained during the hours and days following the eruption, together with transport and dispersion calculations with an atmospheric transport and dispersion model.…”